On Ship Motions and Waves in Navigable Channels with Particular Reference to the Experiments of John Scott Russell: 1834–1835

The speed of a ship which is towed in a channel of restricted width and depth, such as a canal or river, depends on the towing force but it is also influenced by other factors including fluid friction, channel geometry and the blockage factor (the ratio of the cross-sectional area of the ship to that of the channel). If speed steadily increases, a ship may move through three speed ranges namely, the sub-critical, critical and super-critical speed ranges. The lower critical speed is reached at the change from the sub-critical to the critical speed range and the upper critical speed at the change from the critical to the super-critical speed range. 2, 3